[ Response: Not sure what you are pointing to specifically, but I stand = by that statement. The relevant IPCC summary (Chp 2. p185) is as follows:

Since the dominant aspect of land cover change since 1750 has been deforestation in temperate regions, the overall effect of anthropogenic land cover change on global temperature will depend largely on the relative
importance of increased surface albedo in winter and spring (exerting a cooling) and reduced evaporation in summer and in the tropics (exerting a warming) (Bounoua et al., 2002). Estimates of global temperature =
responses from past deforestation vary from 0.01=B0C (Zhao et al., 2001) to = =960.25=B0C
(Govindasamy et al., 2001a; Brovkin et al., 2006). If cooling by = increased surface albedo dominates, then the historical effect of land cover = change may still be adequately represented by RF. With tropical deforestation becoming more significant in recent decades, warming due to reduced evaporation may become more significant globally than increased surface albedo. Radiative forcing would then be less useful as a metric of climate change induced by land cover change recently and in the future.

and (p184)

On the basis of the studies assessed here, including a number of new estimates since the TAR, the assessment is that the best estimate of RF relative to 1750 due to land-use related surface albedo change should =
remain at =960.2 =B1 0.2 W m=962.

Thus while there are complexities and uncertainties involved, the best estimate is that LCC has been a cooling effect historically. I still don’tknow where the US statistic that was quoted in #289 comes from. – gavin]

My Reply

Gavin is using old information. New research has shown a significant warming effect for a number of landscape conversions; e.g. see

Fall, S., D. Niyogi, A. Gluhovsky, R. A. Pielke Sr., E. Kalnay, and G. Rochon, 2009: Impacts of land use land cover on temperature trends over the continental United States: Assessment using the North American Regional Reanalysis. Int. J. Climatol., DOI: 10.1002/joc.1996. https://pielkeclimatesci.files.wordpress.com/2009/08/r-329.pdf

from the abstract

“….most of the warmingtrends that we identify can be explained on the basis of LULC changes, we suggest that in addition to considering the greenhouse gases–driven radiative forcings, multi-decadal and longer climate models simulations must further include LULC changes.”

“Across the (United States) as a whole, approximately 50 percent of the warming that has occurred since 1950 is due to land use changes (usually in the form of clearing forest for crops or cities) rather than to the emission of greenhouse gases,” Stone said. “Most large U.S. cities … are warming at more than twice the rate of the planet as a whole — a rate that is mostly attributable to land use change.”

******END OF UPDATE****

There is a response by Gavin Schmidt on Real Climate with respect to the role of land use change on the attribution of surface air temperature trends [thanks to Charlie Allen for alerting us to it!]. While Gavin has expertise in global climate modeling, his reply illustrates his lack of expertise on the role of landscape processes within the climate system, and, in this example, with respect to the role of land use/land cover change on long temperature trends.

The text from Real Climate is

1. CCPO @258 – you quoted Gavin as saying “Note. global land use effects result in a cooling because the biggest issue is the chopping down of forest (dark) to make cropland (bright)”

Well, that’s not actually true. Here’s a press release for a new paper from Georgia Tech, showing how 50% of the warming across the US is due to land use changes.

Original reference for Gavin’s comment was from Edward’s post @95.

Cheers.

[Response: A statement in a press release is not a scientific result and the paper referred to does not show this to be true (and in fact I doubt very much that it is true). There are many papers on the global impacts of land cover change – Pondgratz et al is good, and all such papers show that land use at the global scale drives a cooling. – gavin]

“….the mean decadal rate of warming across the urban stations is significantly higher than that of rural stations. Averaged over the full period, the mean decadal rate of warming for urban stations was found to be 0.08 °C higher than that of rural stations. This average rate of heat island growths i.e., urban warming in excess of the rural trends rises to 0.20 °C/decade over the most recent 20 years of observation.”

and

“The increasing divergence between rural and urban temperature trends in U.S. cities highlights the limitationsof a climate policy framework focused on emissions reductions alone. If land use change is the dominant agent of climate forcing at the urban scale, Kyoto-based emissions trading schemes may fail to sufficiently safeguard human health in the most heavily populated regions of the planet. It is important to emphasize, however, that the phrase “urban heat island effect,”muchlike the phrase “greenhouse effect,” is a misnomer…The physical mechanisms underlying warming trends in cities are limited neither to urban areas nor to small geographic regions. Rather, changes in surface moisture and energy balances accompanying land conversion processes across large swaths of the planet’s land area are giving rise to changes in climate that may be of the same order of magnitude as changes brought about through the emission of GHGs. As such, the urban heat island effect should be understood to be only the most visible manifestation of a larger phenomenon occurring across multiple geographic scaless a phenomenon better characterized as a “green loss effect” than as something unique to urban areas.”

This reply by Gavin, besides ignoring (e.g. Fall et al 2009) and his trivializing (e.g. Stone Jr 2009) peer reviewed papers that disagree with his perspective, his comment also shows that he has learned little from the exposure of the inappropriate attempt by Phil Jones and colleagues to serve as gatekeepers to climate science issues.

Since Gavin Schmidt is not a recognized expert on the role of land use/land cover change, he should have sought a qualified climate scientist to address the comment by CCPO. Instead, he perpetuates the biased and often inaccurate presentation of climate views on Real Climate.